"We were all dissidents and collaborators," said Vladimir Ashkenazy, drawing on his own experiences of life in the Soviet Union, at the start of the latest concert in the South Bank's uncompromising examination of the careers of Prokofiev and Shostakovich under Stalin. Ashkenazy admitted he had "been asked to say a few words about this evening's programme". Propaganda music - mostly for film and shown with the relevant clips - was placed against Shostakovich's Chamber Symphony. It is an orchestration, prepared by Rudolf Barshai, of the composer's harrowing Eighth String Quartet - "the opposite of what he had to write in order to be left alone", Ashkenazy reminded us.

The series itself raises more questions than it can answer. To hear Prokofiev's Toast to Stalin next to chunks of his score for Eisenstein's Ivan the Terrible is to experience doubts about his sincerity. Prokofiev hymns Stalin in a passionate musical language close to that of Romeo and Juliet. Ivan the Terrible, one of Prokofiev's greatest scores, revives the operatic vastness of Mussorgsky's historical chronicles. Dissidence hovers, however, behind both. Prokofiev sets the text of the Toast in such a way that the words are inaudible. Ivan the Terrible is rooted in the progressions of Orthodox Church music, itself suspicious in Stalin's Russia.

Shostakovich's propaganda was represented by excerpts from the soundtracks for two MosFilm epics, The Unforgettable Year 1919 and The Fall of Berlin. Musically the tone of 1919 is one of exhausted compliance. The final scenes of The Fall of Berlin, meanwhile, show Stalin's unhistorical arrival in Berlin at the end of the second world war, a sequence modelled on Leni Riefenstahl's depiction of Hitler's arrival in Nuremberg in The Triumph of the Will. The jingoism that follows is disquieting.

This was made all the more difficult by the gloom generated by the war in Iraq. The Fall of Berlin contains a chilling reminder that the arbiters of death, whatever their individual stances, use a comparable rhetoric. When Stalin announces that "from this moment, history opens its doors to the freedom of peoples", he sounds scarily like George Bush.

The mood intensified with the Chamber Symphony after the interval. The original quartet was triggered by Shostakovich's visit to Dresden in 1960 and is dedicated to "the victims of war and fascism". It was performed in a darkened auditorium. Though Barshai's arrangement sometimes replaces rage with elegy, the impact was shattering.